In this circuit, the LCD terminals are associated with the Arduino pins as per the table beneath.

LCD Pin     Arduino Pin

    RS               13

    EN               12

    D4               11

    D5               10

    D6                9

    D7                8

the LCD terminals are connected with the Arduino sticks as displayed by above table. Associate the outer two terminals of the potentiometer to 5V and ground, and the center terminal to stick 3 of LCD. Turning the potentiometer controls the magnificence of the LCD setting brightening.